A rotary type expander has been known as an expander used for the purpose of recovering the energy of expansion of the refrigerant of a refrigeration cycle apparatus when it expands.
The configuration of a conventional rotary type expander as described in JP 8-338356 A will be described below. For simplicity in illustration, the expander of one piston type will be described.
FIG. 14 is a vertical cross-sectional view illustrating the configuration of a conventional rotary type expander 100, and FIG. 15 is a horizontal cross-sectional view of the expander shown in FIG. 14, taken along line D1-D1. A power generator 101 includes a stator 101a fixed to a closed casing 102 and a rotor 101b fixed to a shaft 103 and generates an electromotive force between the rotor 101b and a coil of the stator 101a by rotation of the rotor 101b to obtain electric power. The shaft 103 penetrates through a cylinder 104 and is supported rotatably by bearings 105, 106. The shaft 103 is provided with an eccentric portion 103a. A piston 107 disposed in the interior of the cylinder 104 is fitted to the eccentric portion 103a. Inside the shaft 103, an axially extending flow passage 103b is provided along the axis of the shaft 103, and a radially extending flow passage 103d connecting the axially extending flow passage 103b and an opening portion 103c is provided in the eccentric portion 103a. 
As illustrated in FIG. 15, a fitting groove 107a is formed in the outer circumferential surface of the piston 107, while a vane groove 104a is formed in the cylinder 104. A vane 108, which is supported reciprocably by the vane groove 104a, is fitted to the fitting groove 107a at its leading end, and it is firmly in contact with the piston 107 at all times by a force resulting from a spring 109 and a force resulting from the pressure difference between the leading end side and the back side of the vane 108. A crescent-shaped space formed by the cylinder 104 and the piston 107 is divided into two working chambers 110a and 110b by the vane 108. An intake port 107b provided in the piston 107 is connected to the working chamber 110a, and a discharge port 104b provided in the cylinder 104 is connected to the working chamber 110b. 
A high pressure working fluid flows into the interior of the closed casing 102 through an intake pipe 111, passes through the axially extending flow passage 103b and the radially extending flow passage 103d of the shaft 103, and thereafter reaches the opening portion 103c. The opening portion 103c rotates along with the rotational motion of the shaft 103, while the piston 107 performs an eccentric rotational motion that does not accompany self rotation, in other words, what is called a swing motion. As a result, the intake port 107b provided in the piston 107 and the opening portion 103c provided in the eccentric portion 103a are connected and disconnected repeatedly along with the rotational motion of the shaft 103. While the opening portion 103c and the intake port 107b are being connected, the working fluid is taken into the working chamber 110a. Thereafter, when the opening portion 103c and the intake port 107b are disconnected, an intake stroke finishes. The working fluid expands with the pressure lowering, and rotates the shaft 103 in a direction in which the internal volume of the working chamber 110a enlarges, thus driving the power generator 101. As the shaft 103 rotates, the working chamber 110a shifts to the working chamber 110b, and when it connects with the discharge port 104b, an expansion stroke finishes. The working fluid, the pressure of which has been lowered, is discharged through the discharge port 104b to a discharge pipe 112.
The principle by which the vane 108 can make contact firmly with the piston 107 will be described. FIG. 16 is an enlarged horizontal cross-sectional view taken along line D1-D1 of the expander shown in FIG. 14. Referring to FIG. 16, the piston 107 is at what is called the top dead center, and the vane 108 is in such a condition that it is pressed into the vane groove 104a most inwardly. Reference characters A and B designate edges formed by the round surface on the leading end side and the side faces of the vane 108, and C and D designate edges formed by the back surface and the side faces of the vane 108. The radius of the round surface on the leading end side of the vane 108 is smaller than the radius of the fitting groove 107a of the piston 107, and therefore, the round surface on the leading end side of the vane 108 makes contact with the fitting groove 107a of the piston 107 at a point E. The surfaces AE, BE on the leading end side of the vane 108 face the space connected to the working chamber 110a. Accordingly, the pressure that acts on the round surface on the leading end side of the vane 108 (i.e., the surface AB) is the pressure in the working chamber 110a. The pressure in the working chamber 110a equals a discharge pressure Pd because the working chamber 110a is connected to the discharge port 104b. On the other hand, the pressure that acts on the back surface CD of the vane 108 is the internal pressure in the closed casing 102, which always equals a suction pressure Ps. Accordingly, because of the pressure difference therebetween, the vane 108 receives a force in a direction such that it is brought into firm contact with the piston 107. At the top dead center, the direction of motion of the vane 108 reverses from the direction inwardly of the vane groove 104a to the direction outwardly thereof, and therefore, the inertial force acting on the vane 108 works in a direction in which the leading end of the vane 108 comes off from the piston 107. However, because of the force resulting from the pressure difference, the vane 108 is allowed to be firmly in contact with the piston 107 with a sufficient margin.
The spring 109 is an auxiliary component for bringing the vane 108 into firm contact with the piston 107 until the pressure difference between the suction pressure Ps and the discharge pressure Pd is produced upon starting. Assuming that the expander is the one used for the refrigeration cycle using carbon dioxide as the working fluid and the vane 108 is made of steel with a height of 10 mm, a width of 4 mm, and a length of 20 mm, wherein the suction pressure Ps is 100 kgf/cm2 and the discharge pressure Pd is 50 kgf/cm2, then the force acting on the vane 108 by the pressure difference is 20 kgf. In addition, assuming that the spring 109 is a coil spring in which its maximum bending amount is 6 mm and the outer diameter thereof is 4 mm, which is the same as the width of the vane 108, the spring force is about 0.3 kgf since the spring constant of a spring of this class is 0.05 kgf/mm at best. On the other hand, when the vane 108 undergoes a simple harmonic motion at 90 Hz with an amplitude of 3 mm, the inertial force is about 0.6 kgf. Thus, it will be understood that, especially when operated at high speed, such as at 90 Hz, the force of the spring 109 is smaller than the inertial force of the reciprocating motion of the vane 108 and the force pressing the vane 108 toward the piston 107 by the pressure difference is required.
Next, the configuration of a conventional rotary type expander, such as the one shown in “Strategic Development of Technology for Efficient Energy Utilization—Development of Two Phase Flow Expander/Compressor for a CO2 Air Conditioner,” a report issued in March 2004 by the New Energy and Industrial Technology Development Organization, will be described below. It should be noted that the rotary type expander shown in the just-mentioned report has the same fundamental configuration as that of the compressor shown in JP 2003-343467 A, although the flow of the refrigerant and the direction of rotation of the shaft are opposite.
FIG. 17 is a vertical cross-sectional view illustrating the configuration of a conventional rotary type expander 200. FIG. 18A is a horizontal cross-sectional view of the expander shown in FIG. 17, taken along line D2-D2. FIG. 18B is a horizontal cross-sectional view of the expander shown in FIG. 17, taken along line D3-D3. A power generator 201 includes a stator 201a fixed to a closed casing 202 and a rotor 201b fixed to a shaft 203. The shaft 203 penetrates through a first cylinder 205 and a second cylinder 206 that are partitioned by an intermediate plate 204 so as to be independent of each other, and is supported rotatably by bearings 207, 208. A first eccentric portion 203a and a second eccentric portion 203b that are off-centered in the same direction with respect to the axis of the shaft 203 are provided vertically along the axis of the shaft 203. A first piston 209 disposed in the interior of the first cylinder 205 is fitted to the first eccentric portion 203a. A second piston 210 disposed in the interior of the second cylinder 206 is fitted to the second eccentric portion 203b. 
The heights and diameters of the first cylinder 205 and the first piston 209 as well as the second cylinder 206 and the second piston 210 are set so that the crescent-shaped space formed by the first cylinder 205 and the first piston 209 becomes smaller than the crescent-shaped space formed by the second cylinder 206 and the second piston 210. In the example shown in FIG. 17, the inner diameter of the first cylinder 205 and the inner diameter of the second cylinder 206 are equal to each other, the outer diameter of the first piston 209 and the outer diameter of the second piston 210 are equal to each other, and the height of the second cylinder 206 is greater than the height of the first cylinder 205. This configuration is followed also in some of the embodiments of the present invention.
As illustrated in FIGS. 18A and 18B, vane grooves 205a and 206a are formed in the first cylinder 205 and the second cylinder 206, respectively. A first vane 211 and a second vane 212 are supported reciprocably by the vane groove 205a and 206a, respectively. Each of them is brought into firm contact with the respective pistons 209 and 210 by a force resulting from springs 213 and 214 and a force resulting from the pressure difference between the leading end side and the back side of the vanes 211 and 212. A crescent-shaped space formed by the first cylinder 205 and the first piston 209 is divided into working chambers 215a, 215b by the first vane 211. Likewise, a crescent-shaped space formed by the second cylinder 206 and the second piston 210 is divided into working chambers 216a, 216b by the second vane 212. An intake port 205b (intake passage) provided in the first cylinder 205 is connected to the working chamber 215a (first intake-side space). The working chamber 215b (first discharge-side space) and the working chamber 216a (second intake-side space) are connected by a through hole 204a (connecting passage) provided in the intermediate plate 204 so as to pass in between the first vane 211 and the second vane 212 diagonally, to form a single space. A discharge port 206b (discharge passage) provided in the second cylinder 206 is connected to the working chamber 216b (second discharge-side space).
A high pressure working fluid flows into the interior of the closed casing 202 through an intake pipe 217, and is taken into the working chamber 215a of the first cylinder 205 through the intake port 205b. The internal volume of the working chamber 215a increases according to the rotational motion of the shaft 203, shifting to the working chamber 215b that is connected to the through hole 204a, and an intake stroke finishes. The working chamber 215b connects with the working chamber 216a of the second cylinder 206 through the through hole 204a, forming a single working chamber. The high pressure working fluid rotates the shaft 203 in a direction in which the internal volume of the working chamber connected as a whole increases, in other words, in a direction in which the internal volume of the working chamber 215b decreases but the internal volume of the working chamber 216a increases, to drive the power generator 201. As the shaft 203 rotates, the working chamber 215b disappears, the working chamber 216a shifts to the working chamber 216b, and an expansion stroke finishes. The working fluid whose pressure has been lowered is discharged through the discharge port 206b to the discharge pipe 218.
In FIGS. 18A and 18B, which has been referred to in the description above, the rotational positions of the respective vane grooves 205a, 206a of the first cylinder 205 and the second cylinder 206 are the same, but this is not always necessary. FIG. 19 is a vertical cross-sectional view illustrating the configuration of a conventional rotary type expander 400 when the vane grooves 205a, 206a are at different rotational positions. FIG. 20A is a horizontal cross-sectional view of the expander shown in FIG. 19, taken along line D4-D4. FIG. 20B is a horizontal cross-sectional view of the expander shown in FIG. 19, taken along line D5-D5. The term “rotational position” herein refers to an angular position around the shaft 203.
The position of the vane groove 205a of the first cylinder 205 is rotated about 30 degrees with respect to the vane groove 206a of the second cylinder 206. By doing so, the through hole 204a to be provided in the intermediate plate 204 can be provided perpendicular to the intermediate plate 204, and moreover, the intermediate plate 204 does not need to be made thick for providing the diagonal through hole 204a. This makes it possible to reduce the internal volume of the through hole 204a significantly and lower the amount of the working fluid remaining the through hole 204a, thereby preventing the efficiency decrease.
The principle by which the first vane 211 and the second vane 212 are brought into firm contact with the first piston 209 and the second piston 210, respectively, will be described below. FIG. 21A is a horizontal cross-sectional view of the expander shown in FIG. 17, taken along line D2-D2, and FIG. 21B is a horizontal cross-sectional view of the expander shown in FIG. 17, taken along line D3-D3.
Referring to FIG. 21A, the first piston 209 is at what is called the top dead center, and the first vane 211 is positioned so that it is pressed into the inward most part of the vane groove 205a. Reference characters A and B designate edges formed by the round surface on the leading end side and the side faces of the first vane 211, and C and D designate edges formed by the back surface and the side faces of the first vane 211. The round surface of the leading end side of the first vane 211 makes contact with the first piston 209 at a point E. The pressure that acts on the round surface on the leading end side of the first vane 211 is the pressure in the working chamber 215a. The pressure in the working chamber 215a equals the suction pressure Ps because the working chamber 215a is connected to the intake port 205b. On the other hand, the pressure that acts on the back surface CD of the first vane 211 is the internal pressure in the closed casing 102, which always equals the suction pressure Ps. Accordingly, there is no pressure difference between the leading end side and the back side of the first vane 211, and the force resulting from pressure difference, which causes the first vane 211 to bring into firm contact with the first piston 209, does not act on the first piston 209. At the top dead center, the direction of motion of the first vane 211 reverses from the direction inwardly of the vane groove 205a to the direction outwardly thereof, and therefore, the inertial force acting on the first vane 211 works in a direction in which the leading end of the first vane 211 comes off from the first piston 209. However, since no force resulting from the pressure difference works, it is necessary to press the first vane 211 by a spring 213 so as not to move away from the first piston 209. As will be appreciated from the fact that the inertial force of the vane 108 was found to be greater than the force of the spring 109 in the trial calculation for the inertial force of the vane 108 and the force of the spring 109 in the conventional rotary type expander 100 shown in FIGS. 14 to 16, the force of the spring 213 is not necessarily sufficient for bringing the first vane 211 into firm contact with the first piston 209. For this reason, it is necessary to design the first vane 211 to have a smaller mass so that the inertial force of the first vane 211 becomes smaller than the force of the spring 213, for example, by changing the material for the first vane 211 from steel to carbon or by making the shape thereof smaller. In another way, as illustrated in FIG. 22, it is possible to employ the configuration in which the vane cannot be separated from the piston by using a swing piston 219 in which the vane is integrally formed with the piston.
On the other hand, referring to FIG. 21B, the second piston 210 is at what is called the top dead center, and the second vane 212 is positioned so that it is pressed into the inward most part of the vane groove 206a. Reference characters A and B designate edges formed by the round surface on the leading end side and the side faces of the second vane 212, and C and D designate edges formed by the back surface and the side faces of the second vane 212. The round surface of the leading end side of the second vane 212 makes contact with the second piston 210 at a point E. The pressure that acts on the round surface on the leading end side AB of the second vane 212 is the pressure in the working chamber 216b. The pressure in the working chamber 216b equals the discharge pressure Pd because the working chamber 216b is connected to the discharge port 206b. On the other hand, the pressure that acts on the back surface CD of the second vane 212 is the internal pressure in the closed casing 202, which always equals the suction pressure Ps. Accordingly, because of the pressure difference therebetween, the second vane 212 receives a force in a direction such that it is brought into firm contact with the second piston 210. At the top dead center, the direction of motion of the second vane 212 reverses from the direction inwardly of the vane groove 206a to the direction outwardly thereof, and therefore, the inertial force acting on the second vane 212 works in a direction in which the leading end of the second vane 212 comes off from the second piston 210. However, because of the force resulting from the pressure difference, the second vane 212 is allowed to be firmly in contact with the second piston 210 with a sufficient margin. As in the expander shown in JP 8-338356 A, the spring 214 is an auxiliary component for bringing the second vane 212 into firm contact with the second piston 210 until the pressure difference between the suction pressure Ps and the discharge pressure Pd is produced upon starting.